Optimized Profile Descents (OPDs) or Continuous Descent Approaches may use idle or near-idle thrust during descents to reduce fuel consumption, engine noise and carbon emissions. With Optimized Profile Descents, aircraft may descend continuously from cruise altitude to the bottom of descent or to an initial approach fix without level path segments. However, to utilize OPDs without reducing the traffic throughput around an airport, Air Traffic Control may impose an RTA at a metering waypoint to safely merge incoming traffic. If idle thrust is used during the OPD, the descent profile is a function of not only aircraft speed, aircraft weight, wind and temperature, but also aircraft platforms and engine types. Therefore, the idle descent profile may vary from one aircraft to another and from one flight to another flight.
One highly efficient performance characteristic of a transport category aircraft may include a constant cruise phase followed by an idle-power descent from cruise altitude to the landing. This idle-power descent may include a constant Mach descent phase, a constant calibrated airspeed (CAS) descent phase, a deceleration from constant CAS to a statutory speed (e.g., 250 knots), a 250 knot descent phase, a deceleration to final approach speed, and a landing. One goal for maximum efficiency may include an idle power descent from a Top of Descent (TOD) point (often 40,000 feet mean sea level (MSL)) to 1000 feet above ground level (AGL) where engines must normally be spooled up for landing and possible missed approach. This most efficient idle-power descent, however, is often unavailable due to a variety of path constraints including additional traffic in the terminal area.
During aircraft transition from en route to landing, air traffic controllers may frequently issue instructions (or clearances) to change aircraft trajectories based on this additional traffic. These instructions may include temporary altitude assignments, increasing or decreasing speed adjustments, and temporary off-course lateral vectoring. These instructions enable traffic controllers to manage air traffic flow while ensuring proper aircraft separation and flight safety. However, these controller instructions cause inefficiencies in performance requiring aircraft to execute suboptimal maneuvers, such as stair-step descents. A stair-step descent burns significantly more fuel and generates more carbon emissions and engine noise than an uninterrupted OPD because OPDs use idle or near-idle thrust to execute a smooth speed-and-altitude profile during the descent phase of flight, while complying with multiple path constraints.
To enable OPDs without reducing traffic capacity throughout the Terminal Radar Approach Control (TRACON) area, a RTA constraint is usually imposed by air traffic controllers on a metering waypoint on the boundary of the TRACON area or on an Initial Approach Fix (IAF) to enable safe merging of air traffic. Therefore, upon receiving the RTA in-flight, the onboard Flight Management System (FMS) must be able to quickly construct the 4-dimensional (4-D) trajectory of an OPD in compliance with the assigned RTA.
A 95% confidence level may be one requirement by Air Traffic Control (ATC) to ensure each aircraft receiving a RTA is able to comply. Systems meeting the 95% confidence level may enjoy preferential treatment or exclusive use of a particular published arrival procedure.
A maximum performance OPD may be the best case scenario based on fuel economy, carbon emissions, and cost to the operator. However, the maximum performance idle descent OPD may not comply with the traffic clearance requirements of the local TRACON.
Consequently, a need exists for a system and related method combining the benefits of a maximum performance and RTA compliant OPD with the requirement for predictability by an air traffic control tasked with traffic separation.